1. Field of the Invention
The present invention relates to a digital video signal processing apparatus, and more particularly, to a digital video signal processing apparatus and method for two-dimensional Y/C separation.
2. Description of the Related Art
The video signal prepared for television (TV) broadcast contains two major parts commingled, the luminance Y (makes a black and white picture in full detail) and chrominance C (coloration with not quite all the detail). This method is used instead of red, green, and blue sub-signals in order to get the best looking picture that can be transmitted in the limited bandwidth of the broadcast channel. Every TV receiver and VCR must contain a filter to separate the luminance and color (Y and C) again. Less than perfect Y/C separators lose resolution—horizontal, vertical, or both. Also there are artifacts such as rainbow swirls where thin stripes should be, and crawling dots where patches of different colors meet.
Thus, the display of a color TV signal transmitted using either the NTSC or PAL standard includes a device for processing a CVBS (Composite Video Blanking Sync) signal which is a composite of a Y (luminance) signal and a C (chrominance) signal. The C signal is quadrature-amplitude-modulated with a predetermined subcarrier frequency and thus the characteristic of the C signal is determined by its frequency and phase characteristics. Accordingly, a digital video signal processing apparatus at a receiving end separates Y and C signals with reference to the characteristic of the C signal and outputs separated Y and C signals (e.g. called S-video).
FIG. 1 is a block diagram of a conventional video signal processing apparatus 100. Referring to FIG. 1, the video signal processing apparatus 100 includes a comb filter 110, a one-dimensional bandpass filter (1D-BPF) 120, a weight determination unit 130, a combiner 140, and a subtracter 150. The comb filter 110 vertically band-pass-filters an input video signal and the 1D-BPF 120 horizontally band-pass-filters the input video signal. The weight determination unit 130 determines weights of the output of the comb filter 110 and the output of the 1D-BPF 120 with reference to vertical/horizontal correlation and the phase of a C signal. The combiner 140 combines the output signals of the comb filter 110 and 1D-BPF 120 using the weights to generate a C signal. The subtracter 150 subtracts the C signal from the input CVBS signal to generate a Y signal.
FIG. 2 is a block diagram of another conventional video signal processing apparatus 200. Referring to FIG. 2, the video signal processing apparatus 200 includes a two-dimensional bandpass filter (2D-BPF) 210, a subtracter 220, and a post-processor 230. The 2D-BPF 210 performs a two-dimensional convolution to extract a C signal. The extracted C signal and a Y signal generated by the subtracter 220 are processed by the post-processor 230. When the 2D-BPF 210 carries out Y/C separation incorrectly, the post-processor 230 compensates the Y/C signal to generate a compensated Y and C signals.
In conventional Y/C separation techniques, Y/C separation is performed based on comb filtering when the edge of a detected image has high vertical correlation but Y/C separation is carried out based on 1D bandpass filtering when the detected edge has high horizontal correlation. As described above, when selecting one of these filtering methods according to a conventional Y/C separation technique, system performance largely depends on a threshold used for edge detection. Thus, Y/C separation can be executed incorrectly or unstably when the filtering method is wrongly selected due to inaccurate edge detection. Conventional techniques that do not select one of the filtering methods but combine the results of the filtering operations can solve this problem to some extent. However, these techniques are based on horizontal or vertical one-dimensional filtering, and thus, artifacts may remain in the generated signal due to the inconstant edge directions.
In other words, in the case where the direction in which the edge of an image extends is not uniform, cross-luma, which occurs when a C component exists in the separated Y signal, resulting in dotted artifacts, and cross-color, which occurs when a Y component exists in the separated C signal, resulting in a rainbow pattern artifact, can appear on a displayed image when Y/C separation is not properly performed by comb filtering or 1D bandpass filtering selected discontinuously.